The present invention relates to a method and apparatus for streamlining in a communication system with a core network and an access network receiving a plurality of data streams from a subscriber unit. The invention is applicable but not limited to a cellular mobile radio communication system such as the Universal Mobile Telecommunication System (UMTS) currently under standardisation.
In a cellular mobile communication system, such as for example the Global System for Mobile communication (GSM) or the Universal Mobile Telecommunication System (UMTS), each of the subscriber units communicate with typically a fixed base station. Communication from the subscriber unit to the base station is known as uplink and communication from the base station to the subscriber unit is known as downlink. The total coverage area of the system is divided into a number of separate cells each covered by a single base station. The cells are typically geographically distinct with an overlapping coverage area with neighbouring cells. As a subscriber unit moves from the coverage area of one cell to the coverage area of another cell, the communication link will change from being between the subscriber unit and the base station of the first cell to being between the subscriber unit and the base station of the second cell. This is known as a handover. Specifically, some cells may lie completely within the coverage of other larger cells.
All base stations are interconnected by a network. This network comprises communication lines, switches, interfaces to other communication networks, various controllers required for operating the network and the base stations themselves. A call from a subscriber unit is routed through the network to the destination specific for this call. If the call is between two subscriber units of the same communication system the call will be routed through the network to the base station of the cell in which the other subscriber unit is currently located. A connection is thus established between the two serving cells through the network. Alternatively, if the call is between a subscriber unit and a telephone connected to the Public Switched Telephone Network (PSTN) the call is routed from the serving base station to the interface between the cellular mobile communication system and the PSTN. It is then routed from the interface to the telephone by the PSTN.
In some communication systems, such as the Universal Mobile Telecommunication System (UMTS) currently under development, the network is split into a core network and an access network.
The core network comprises the necessary switching and interfaces to serving networks such as the PSTN, the Internet, other cellular systems (e.g. between GSM and UMTS), mobile station register entities (such as the Home Location Register and Visitors Location Register used in GSM). The core network would ideally require no knowledge of the technology (e.g. radio interface) used in the access network.
In the case of a cellular mobile communication system, the access network comprises those elements specific to a particular radio interface e.g. mobiles stations, the base stations used to transmit and receive the radio signals from the mobile stations, and the controllers used to route the calls between base stations and the core network.
Typically, the access network will comprise a plurality of access systems with different access nodes. An access system typically comprise an access controller controlling a number of access node where each access node comprises one or more base stations and possibly one or more site controllers controlling a number of base stations.
In for example a cellular radio communication system, the subscriber unit can typically for at least part of the time be received by more than one radio receiver. In some communication systems such as the Wideband Code Division Multiple Access (WCDMA) system defined for UMTS, the signal from the subscriber unit may simultaneously be demodulated in a plurality of these receivers. A number of received data streams representing the same data stream transmitted from the subscriber unit will thus be generated either in the same access node or possibly in a plurality of access nodes. A typical example where a plurality of parallel data streams from the same subscriber unit are generated in different access nodes is during handover when the subscriber unit is moving from one cell with one access node to a different cell with a different access node. In order to attain optimum performance, the parallel data streams generated are combined into a single data stream representing the transmitted data stream from the subscriber unit. One methods of combining data streams include Maximum Ratio Combining or Selection Combining, the last method simply consisting in selecting the data stream with the lowest error rate. Combining data streams from more than one access node during handover is known as a soft handover. Further description can be found in for example xe2x80x98Spread Spectrum CDMA Systems for Wireless Communicationsxe2x80x99 by Savo Glisic and Branka Vucetic, Artech House Publishers, 1997, ISBN 0-89006-858-5.
Combining the plurality of data streams into a single data stream is typically done in the access network before the single data stream is routed through a connection to the core network. The optimal routing of the data streams within the access network and to the core network will vary depending on which access nodes are receiving data streams from the subscriber unit. In most cellular mobile communication systems the cost of routing data through the network is very significant. Typically, the optimal routing is therefore given as the routing of the data streams which incurs the lowest cost. Alternatively, it could be the routing resulting in the lowest delay or the lowest bandwidth consumption.
As the subscriber unit moves between different cells and thus different access nodes the optimal routing and the optimal access point for connection to the core network will change. It is therefore necessary to change the routing in the access network and the access point to the core network as the subscriber unit moves. This is known as streamlining.
If the streamlining is inefficient, it can result in significantly increased cost for example due to increased bandwidth requirements of the access network. Also an inefficient streamlining can result in interruptions in the data stream and thus cause interruptions in the communication from the subscriber unit.
A significant advantage can thus be obtained from an efficient streamlining in a system with a core network and an access network with a plurality of access systems.
The invention seeks to provide a system for performing efficient streamlining in a communication system with a core network and an access network with a plurality of access systems.
According to a first aspect of the invention, there is provided a method of streamlining in a communication system with a core network, an access network with at least a first and a second access system and at least one subscriber unit. At least one of the first and second access systems generates a plurality of data streams from a signal received from the subscriber unit, the plurality of data streams being combined to a first combined data stream in the first or second access system and the first combined data stream being transmitted to the core network through a first connection between the first access system and the core network. The method comprising the steps of: setting up a second connection from the second access system to the core network in parallel to the first connection, combining a first subset of the plurality of data streams into a second combined data stream and a second subset of the plurality of data streams into a third combined data stream and simultaneously routing the second combined data stream to the core network through the first connection and routing the third combined data stream to the core network through the second connection, switching from the first connection to the second connection in the core network, and terminating the first connection.
Preferably the method includes the step of combining the first subset of the plurality of data streams with the third combined signal after switching to the second connection in the core network and preferably the first subset of the plurality of data streams contains the data streams received by the first access system and the second subset of the plurality of data streams contains the data streams received by the second access system.
According to a feature of the invention, the communication system is a CDMA cellular radio communication system and the access network is a CDMA radio access network.
According to a different aspect of the invention there is provided, an apparatus for streamlining in a communication system with a core network, an access network with at least a first and a second access system and at least one subscriber unit. At least one of the first and second access systems generates a plurality of data streams from a signal received from the subscriber unit, the plurality of data streams being combined to a first combined data stream in the first or second access system and the first combined data stream being transmitted to the core network through a first connection between the first access system and the core network. The apparatus comprising: means for setting up a second connection from the second access system to the core network in parallel to the first connection, means for combining a first subset of the plurality of data streams into a second combined data stream and a second subset of the plurality of data streams into a third combined data stream and simultaneously routing the second combined data stream to the core network through the first connection and routing the third combined data stream to the core network through the second connection, means for switching from the first connection to the second connection in the core network, and means for terminating the first connection.